The present invention relates to wide band impedance transformers with an impedance transformation ratio close to three operating at radio frequencies.
Such transformers are in particular required when three synchronized transmitters, with an output impedance Ro, are to be coupled to the same antenna with impedance Ro. In fact, a coupler is then used which comprises three inputs to which the three transmitters are connected, and an output; but since this output has an impedance Ro/3 it is necessary to insert an impedance transformer having an impedance transformation ratio as close as possible to three between the output of the coupler and the antenna. It is known to use, as impedance transformer with a transformation ratio close to three, a self transformer having an impedance transformation ratio equal to four formed from four coaxial cable sections connected as will be shown in FIG. 1 hereafter. These known impedance transformers, having a transformation ratio fairly different from three, do not then provide good matching. To avoid this when for example, a group of three transmitters would be sufficient, it is known to use four transmitters; thus the transformer with a ratio 4 provides very good matching between the output of impedance Ro/4 of the coupler of the four transmitters and the antenna of impedance Ro. But this is an expensive solution since it leads to using an extra transmitter.